DEAR DOCTOR K:
I was recently diagnosed with Type 2 diabetes. My doctor says I need to have lots of other doctor appointments as a result, including seeing the eye doctor. Can you explain how diabetes affects vision?
Both of the common types of diabetes, Type 1 (which usually begins in childhood) and Type 2 (which usually begins in adulthood), can affect vision in several ways. After 20 years of having Type 2 diabetes, most people have eye problems. But the risk can be reduced, as I’ll explain.
The most serious eye problem resulting from the uncontrolled high blood sugar levels that can occur with diabetes is diabetic retinopathy. It can cause severe vision loss and even blindness.
Diabetic retinopathy occurs when high blood sugar leads to damage of small blood vessels in the retina. (The retina is the light-sensitive tissue in the back of the eye that sends images to the brain.) The damaged vessels leak fluid and blood into the retina. They also can close entirely, robbing the retina of its blood supply. When your doctor looks inside your eyes, he or she looks for the telltale marks and scars that diabetic retinopathy leaves on the retina.
If the fluid or blood leaks near the macula — the part of the retina responsible for sharp, central vision — sight becomes impaired. When fluid leaks into the center of the macula, it can swell, blurring vision. This is called macular edema.
When a damaged blood vessel closes, the retina tries to repair itself by sprouting new blood vessels to replace the damaged ones. That’s another thing your doctor is looking for when he or she looks in your eyes. Unfortunately, these new blood vessels grow abnormally and can cause serious problems. They can extend into the gel-filled compartment of the eye in front of the retina. If these fragile new vessels bleed, they can cause sudden vision loss.
You can help prevent diabetic retinopathy by carefully controlling your blood sugar levels. The other key to prevention is an annual eye exam, which can detect even the earliest signs of retinopathy. It is particularly important to spot the growth of new blood vessels as early as possible, because they can be treated with lasers.
Laser treatments are the standard of care. Focal laser treatments seal off individual blood vessels in macular edema. This slows leakage and decreases fluid around the retina. Scatter laser treatment is used for advanced retinopathy. Laser burns in the outer edges of the retina prevent new blood vessel growth.
A new class of medicines, called anti-VEGF drugs, block a chemical signal that stimulates blood vessel growth. (Examples of these drugs are bevacizumab, ranibizumab and pegaptanib.) They often are used along with laser treatment. I’m proud to say that these powerful new drugs come from research done here at Harvard Medical School several decades ago. Because we have new treatments available to prevent and treat eye damage in people with diabetes, it really is important for you to see the eye doctor regularly.
(This column is an update of one that ran originally in October 2012.)